High efficiency linear amplifier system



April 26, 1966 M. l. JACOB HIGH EFFICIENCY LINEAR AMPLIFIER SYSTEM 3Sheets-Sheet 1 Filed Feb. 25, 1965 NINW mvr-:N'roR Mark I. JacobATToRN%/d% April 26, 1966 M. l. JAcoB HIGH EFFICIENCY LINEAR AMPLIFIERSYSTEM Filed Feb. 25, y1963 5 Sheets-Sheet .2`

M. I. JACOB HIGH EFFICIENCY LINEAR AMPLIFIER SYSTEM Filed Feb. 25, 1:965

April 26, 1966 3 Sheets-Sheet 3 but a high impedance to all harmonicsthereof.

United States Patent O 3,248,663 HIGH EFFICIENCY LINEAR AMPLIFIER SYSTEMMark I. Jacob, Ellicott City, Md., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., 'a corporation of Pennsylvania Filed Feb.25, 1963, Ser. No. 260,758 11 Claims. (Cl. S30-124) This inventionrelates in general to a system for electric amplification and moreparticularly to a system for providing linear amplification ofelectrical signals having amplitude variations at a relatively highover-all operating efficiency.

Briefiy, the problem has existed in providing a high efficiency linearamplifier adaptable to utilize high efficiency solid rstate amplifiersof the type described and claimed in copending applications, Serial No.256,701, filed -February 6, 1963, by T om L. Dennis and Serial No.256,693, filed February 6, 1963, Iby James H. Andreatta, both of whichare assigned to the assignee of the present invention. Whereas priorinventions in the field of linear amplification of electrical signalsare known to provide adequate results, they have been found to beimpractical where high efficiency solid state amplifiers are to beemployed. Solid state amplifiers fof the type referred to above employsemiconductors operated as switches to alternately charge and dischargea network which provides a low impedance to the frequency to be ampliidA itionally the transistors are driven into switching mode by a drivingsignal which saturates the semiconductors when conductive only to thepoint where a minimum saturation internal impedance is provided and thiscondition is maintained throughout the conductive lperiod withoutover-driving the semiconductor lat any time.' Overall operatingefficiencies in the order of 90% or greater are achieved with s-olidstate amplifiers of-this type. It is desirous to utilize amplifierscovered lby the aforementioned inventions in providing a high efficiencylinear solid state amplifier for the amplification of radio fre.- quencysignals in apparatus such as a radio transmitter.

It is an object of the present invention therefore, to provide a highefiiciency linear amplifier for electrical signals. Y

It is another object of the present invention to provide an amplifiersystem for the amplification of radio frequency signals having amplitudevariations in a linear amplifier adapted to utilize high efficiencysolid state amplifier units.

It is a further object of the present -invention for providing a linearampli-fier system for radio frequency signals wherein high efficiencylinear amplification is provided with the use of solid state activeelements.

Briefly, the present invention accomplishes the above-- cited objects byconverting an input signal having amplitude variations into two or moresignals which are shifted in phase with--respect to each other and whereat least one of the signals has a variable phase shift which is afunction of the amplitude variations of the input signal.

. These phase shifted signals are then amplified in high efficiencyamplifiers and then reconverted in an isolating adder network whichtransforms the phase variations into an output signal having amplitudevariations. Stated in another way, the invention converts signalsvarying in amplitude into signals which vary in phase. These signals arethen amplified in constant level amplifier-s utilizing solid stateactive ele-ments and then a reconversion is effected to change the phasevarying constant amplitude amplified signals back into an output signalwhich rcproduces the input signal having amplitude variations inamplified form.

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Further objects and advantages of the invention will become apparent asthe following descriptionproceeds.

For a better understanding of the invention, reference may be had to theaccompanying drawings in which:

FIGURE 1 is a block diagrammatic illustration of one embodiment of thepresent invention;

FIG. 2 is a diagram more fully illustrating the embodiment of FIG. l;

FIG. 3 is a block diagrammatic illustration of another embodiment of thepresent invention;

FIG. 4 is a diagram more fully illustrating the embodiment of FIG. 3;

FIG. 5 is a diagrammatic illustration of yet another embodiment of thepresent invention; and

FIG. 6 is a diagram more fully illustrating the embodiment of FIG. 5.

Referring now to FIG. 1, the first embodiment of the present inventioncomprises a limiter amplifier 14, a variable phase shifter 20, a firstamplifier 28, a phase shifter 22, a second amplifier 30 and a load 36,all interconnected as hereinafter described. A pair of input terminals11 and 12 are included for the application of an input signal. Terminal1I is connected to the limiter amplifier 14 by suitable circuit means15. Terminal 12 is returned to a point of common reference potentialillustrated as ground. The limiter amplifier 14 is coupled to thevariable phase shifter 20 and the 180 phase shifter 22 by means ofsuitable electrical circuit means 17 and 18, respectively. In additionto the connection 17, the variable phase shifter is also coupled to theinput terminal 11 by means of a suitable 1circuit'connection 16.

The variable phase shifter 20 comprises an electrical circuit which willshift the phase of a signal applied thereto in accordance with a controlsignal which is dependent on the amplitude variation of the input signalapplied to input terminals 11 and 12. The variable phase shifter 2t)then, is a voltage variable phase shifter and can be of any type whichare known to those skilled in the art; however, one means for providinga variable-phase shift will 4be more fully illustrated in connectionwith the embodiment shown in FIG. 5 which will be more fully explainedsubsequently.

The variable phase shifter 20 is coupled to the first amplifier 28 Ibyelectrical circuit means 26 and electrical circuit means 24 connects the180 phase shifter 22 to the second amplifier 30. Outputs from the firstand second amplifiers 28 and 30 are coupled to the load 36 by means ofelectrical circuit means 32 and 34 respectively.

The first and -second ampliers 28 and 30 are of the constant level typein that the gain of these amplifiers is s ubstantially constant andmutually equal. Additionally,

amplifiers 28 and 30 are preferably high eliciency solid stateamplifiers of the type previously mentioned with respect to theinventions disclosed in Serial Nos. 256,701 and 256,693, previouslynoted.

. The operation of the embodiment shown in FIG. 1 will now be explained.Reference to FIG. 2 will aid in the explanation since FIG. 2 is a vectordiagram of the magnitude and phase relationship of signals appearing atvarious points in the amplifier system disclosed. In this embodiment, aninput signal E 0 having amplitude variations is applied to the inputterminals 11 and 12. The input signal is applied to the limiteramplifier 14 which produces a constant level signal KE0 irrespective ofthe amplitude of the input signal E 6. The limited signal KE 0 issimultaneously applied to the variable phase shifter 20 and the 180phase shifter 22 by means of the sa prised of the 180 phase shifter 22in combination with the second amplifier 30. The variable phaseshifterreceives the constant level signal KF.6 simultaneously with the inputsignal EU) and shifts the phase angle of the constant level signal KE0to generate a constant level signal shifted in phase where the phase isproportional to the amplitude of the input signal EN). The variablephase shifter then provides a signal KE/@Jra where a=f(|El), and |E| isequal to the scalar magnitude of the input signal E 9. This constantlevel variable phase signal is then amplified in the constant level highefficiency amplifier 28 by a factor of G1 to provide a signal GlK'E/-i-.

The constant level signal KE0 produced by the limiter and applied to the180 phase shifter 22 produces a signal ICE/@+180 This signal is appliedto the second amplifier 30 by means of electrical circuit means 24 andis amplified by a gain factor G2 to produce a signal GzKE/J-i-ISO.

The signals, GlKE/-l-u and GzKE/-l-lSO, from the amplifiers 28 and 30respectively are fed to a load 36 which sums these signals and producesan output signal Eo which reproduces the amplitude variations of theinput signal E0 in amplified form and is the resultant vector quantityof the signals from amplifiers 28 and 30 respectively, according to theequation Since the phase angle (1H-a) of the signal from amplifier 28 isvariable in proportion to the amplitude of the input signal EU), theamplitude sum of the two signals from the constant level high efficiencyamplifiers 28 and 30 will vary in proportion to the amplitude of the'input signal.

Whereas the embodiment disclosed in FIG. 1 results in high efficiencylinear amplification, a more practical embodiment is illustrated in FIG.3 which is similar to the embodiment of FIG. 1 up to the outputs of theamplifiers 28 and 30. In the present embodiment, additional means isincluded for combining the outputs from high efficiency amplifiers 28and 30. A combiner or summing network 45 is illustrated which comprisesa transformer 48 connected to transformer 51 such that the voltagesinduced in the secondaries 49 and 53 of transformers 48 and 51,respectively, do not appear in the respective primaries 47 and 52 of theother. More specifically the end terminals to the primary winding 47 oftransformer 48 is coupled to the first amplifier 28 by means of suitablecircuit means 32 and 33. The secondary winding 49 of transformer 48 iscoupled to a load 36 and an isolation means such that one end terminalof secondary winding 49 is connected by electrical circuit means 55 toone end of the load 36 while the opposite end terminal of secondarywinding 49 is connected to one end of the isolation means 40 byelectrical circuit means 57. The respective opposite ends of the load 36and the isolation means 40 are connected together and returned to groundpotential. The other transformer 51-of the combiner network has itsprimary winding 52 coupled to the second high efficiency amplifier 30 bymeans of suitable electrical circuit means 34 and 35. The secondarywinding 53 has, for example, half the number of turns as its primarywinding and has one terminal connected to the center tap of thesecondary winding 49 while the opposite terminal is returned to groundby means of electrical circuit means 56. The interconnection oftransformers 48 and 51 prevents interaction between the amplifiers 28and 30 and thereby provides a constant load impedance undersubstantially all operating conditions. This network describes what isreferred to in the art as a hybrid circuit. The term, hybrid, is a termused to define a passive isolation network which provides a plurality ofoutputs from one or more non-interacting in- L puts. The term, hybrid,is used in connection with distribution of power to an output load suchas a radio antenna from an output power amplifier.

Accordingly the load 36 may be the load impedance as presented by aradiating antenna for a radio transmitter. The combiner unit 45 isuntuned and, therefore, requires no adjustment with Variations in signalfrequencies within wide limits.

In operation, the embodiment of FIG. 3 operates in the substantiallyidentical manner as the embodiment shown in FIG. 1 up to the combiner45. Designating the signal from the high efliciency amplifier 28H1 andthe signal from the high efficiency amplifier 30E2 where E1 and E2 areimpressed across the primary windings 47 and 52 of transformers 48 and51 respectively, and referring to FIG. 4, which illustrates the vectorrelationship of the voltages concerned with the combiner network 45, thecombiner acts to vectorially add and subtract voltages appearing acrossthe secondary windings 49 and 53. Therefore, 1/2 of the signal El isvectorially added to 1/2 of the signal E2 to provide an output signal Eosuch that On the other half winding of secondary winding 49, 1/2 of thevoltage of the signal E1 is subtracted from 1/2 of the signal E2appearing across secondary winding 53 to provide a signal E1 across theisolator means 40 according to the relationship Referringto FIG. 4, thevector El is a voltage whose phase angle is varying in accordance withthe amplitude variations of the input signal E 0, or IEI. Therefore, thevector El will be of constant magnitude with a changing phase angle of/-f-a. The vector E2 is of a constant amplified magnitude shifted 180from the input signal E 0. Summing the vectors ENZ and EZ/z provides theoutput vector Eo which varies in amplitude according to the amplitudevariations of the input signal `E0 and reproduces the input signal inamplied form.

The vector EI is much less in magnitude than the vector Eo since it isthe resultant vector of subtracting the vector El/Z from Em.

The third and most preferred embodiment of the present invention isillustrated in FIG. 5. Although the basic concept of changing the inputsignal having amplitude variations into a signal which is changing inphase with respect to the amplitude variations of the input signal andthen reconverting the phase variations back into amplitude variationsremain the same, however, the manner in which the phase shift of thesignal is effected is modified.

Referring to FIG. 5 the input signal E 0 is applied to input terminals11 and 12 where terminal 12 is coupled by means of electrical circuitmeans to a phase splitter 21 which separates the input signal into twocomponent signals separated by a phase angle difference of 90. The 90phase splitter 21 may be of any well known phase shift network which iscapable of providing the desired phase shift. The two components of theinput signal can be designated E70-90 and E0. The 90 phase splitter 21is similarly connected to a linear amplier 19 and a limiter amplifier 14to form two signal channels wherein the first signal E70-90 is appliedto linear amplifier 19 through circuit means 25 while the second signalE6 is applied to the limiter amplifier f4 through circuit means 27. Thelimiter amplifier 14 is connected to one terminal of primary winding 61by circuit means 42 while the other terminal of primary winding 61 isreturned to ground. The linear amplifier 19 is connected by suitablecircuit means 43 to the center tap 64 of the secondary winding 62 oftransformer 60. One end terminal of the secondary winding 62 is coupledto a first amplifier 28 by circuit means 54 while the other end terminalof secondary winding 62 is coupled to a second amplifier 30 through thecircuit means 58. The amplifiers 28 and 30 are coupled to the combinernetwork 45 by means of electrical circuit means 32 and 35 respectively,and lastly,

' the combiner is connected to a radiating antenna 75 by means ofcircuit means 55 and also to the isolator means 40 through circuit means57.

With additional reference to FIG. 6 which illustrates vectorrepresentation of the voltage signals at selected points in the system,the two channel signals E/0-90 and E0 are fed to the linear amplifier 19and the limiter amplifier 14, respectively. The linear amplifier 19produces a signal which varies linearly with respect to the amplitude ofthe input signal impressed across the input terminals 11 and 12.Therefore, the signal coming from the linear amplier 19 will have anamplification factor of K such that the signal coming from linearamplifier 19 can be represented as KEN-90. It shouldvbe to thetransformer 60 such that the signal from the limiter amplifier 14 (KE'0)is impressed across the primary winding 61 of the transformer 60 whereasthe signal from the linear amplifier 19 (KE/0-90) is fed to the centertap 64 of thesecondary winding 62 of transformer 60. The transformer 60acts to provide signals at the end terminals of the secondary winding 62that are the sum and difference of the voltages applied across theprimary and the center tap 64. One end terminal ofthe secondary winding62 provides a first intermediate signal El to circuit means 54 vwhich isthe vector summation ofV I The other end terminal of the secondarywinding provides a Isecond intermediate signal E2 to the circuit means58 which is equal tothe difference between KEN2-'90 and The intermediatesignals El and E2 are both varying in phase with respect to the inputsignal E 0 due to the fact that the signal from the linear amplifier 19KE'/09O is varying in amplitude proportional to the inputsignal. Thesignal E1 is fed to a first constant gain amplifier 28 which, forexample, is comprised of a high efficiency linear amplifier utilizingsolid state active elements. The output of the constant gain amplifieramplities the first intermediate signal E1 by `a factor of G1 such thatthe signal fed to the combiner 45 can be designated as G1E1. Likewise,the second intermediate signal E2 is fed to a second constant gainamplifier 30 having a gain substantially equal to the gain of the firstamplifier 28. Likewise,

amplifier 30 is, for example comprised of a high efiiciency linearamplifier utilizing solid state active elements. The signal from theamplifier 30 has an amplification factor of G2 and, accordingly, thesignal fed tothe combiner 45 from the amplifier 30 is designated G2E2.

-and output terminals comprising in combinationzmeans By Way of exampleit should be pointed out with respect to the embodiment of FIG. 5 thatthe over-all operating efiiciency Aof said apparatus which has beenbuilt and tested is in the order of at full output power and secondly,the linearity provided is in the order of 40 db third order distortioncapability. The isolation Iof power dissipated into a lumped load allowsa choice as to the location of high temperature heat sinks. Since thecom-- biner unit is untuned, and therefore requires no adjustment, thesubject invention is capable of operating over wide limits of signalfrequencies.

What has been described, therefore, is an amplifying system which takesa signal varying in amplitude and changes it into one or more constantamplitude phase varying signals which are subsequently amplified inconstant level high eiiciency amplifiers and then are reconverted intoan output signal which is varying in amplitude by means of an untuned,isolating combiner network.

Whereas the apparatus has been shown and described with respect topreferred embodiments thereof which gives satisfactory results it shouldbe understood that changes may be made and equivalents substitutedwithout departing from the spirit and scope of the invention.

What I claim is:

1. An electrical signal amplify-ing system having input and outputterminals comprising in combination: circuit means operably connected tosaid input terminals for converting amplitude variations in a signalapplied to said input terminals into a plurality of s-ignals, saidplurality of signals including one signal which varies in p'hase as afunction of said amplitude variations; amplifier means opera'blyconnected to said circuit means for individually and separatelyamplifying each of said plurality of signals; an isolating combinermeans coupled to said amplifier means for combining said plurality ofsignals amplified into an output signal which varies in amplitudeaccording t-o said signals applied to said input terminals.

2. An electrical signal amplifying system having input operablyconnected to said input terminals for converting amplitude variations ofelectrical signals applied to said `input terminals into a plurality ofsignals one of which has phase variations which are proportional to saidamplitude variations; amplifier means coupled to said means forconverting for individually and separately Iamplifying each of saidplurality of signals, and isolating combiner means coupled to `saidamplifier means for reconverting signals amplified therein into at leastone output signal varying in amplitude according to said signals appliedto said input terminals.

3. An amplifyingrsystem comprising Iin combination: input means; circuitmeans responsive to an input signal applied'to said input means forproviding a rst and a second si-gnal havin-g a predetermined phaserelationship with said input signal and wherein at least one of saidfirst and second signal varies in phase in a manner functionally relatedto the amplitude of said input signal; first amplifier means coupled tosaid circuit means for amplifying said first signal; second amplifermeans coupled t0 said circuit means for amplifying said second signal;and non-interacting load means including a combiner network coupled tosaid first and second second amplifiers for summing signals in saidfirst and second signal channels to provide a resultant output signalwhich is varying in amplitude.

4. An amplifying system having input and output terminals and comprisingin combination: limiter means connected to said input terminals forproviding a constant amplitude signal irrespective of amplitudevariations of signals applied to said input terminals; first phase shiftmeans connected to said limiter means for receiving said constantamplitude signals and including means to receive signals applied to saidinput terminals to shift the phase of said constant amplitude signalsproportionally to the amplitude variations of said signals applied tosaid input terminals; first amplifier means coupled to said first phaseshift means for amplifying said signals having phase variations; secondphase shift means coupled to said limiter means for effecting apredetermined phase shift of said constant amplitude signals; secondamplifier means coupled to said second phase shift means; and meanscoupled to said first and second amplifier means being responsive tosignals amplified thereby to provide an output signal to a load which isthe vector sum of signals from said first and second amplifier means.

S. An electrical amplifying system for an input signal comprising incombination: input'and output terminals; circuit means connected to saidinput terminals for limiting the amplitude of said input signal tosubstantially a constant magnitude to form a limited signal; first phaseshift means connected to said circuit means for varying the phase ofsaid limited signal according to variations in amplitude of said inputsignal; a first amplifier means connected to said first phase shiftmeans for amplifying by a predetermined gain factor said limited signalshifted in phase; second phase shift means connected to said circuitmeans, for providing substantially a 180 fixed phase shift to saidlimited signal; second amplifier means connected to said second phaseshift means and having a gain factor substantially equal to said gainfactor of said first amplifier means; and means operably connected tosaid first and said second amplifier means for adding signals amplifiedtherein in vector relationship to produce an output signal to saidoutput terminals which is varying in amplitude according to theamplitude variations of said input signal.

6. An amplifying system for radio frequency signals comprising incombination: means responsive to an amlplitude varying input signal forproviding at least two signals which are changed in phase with respectto the phase of said input signal, at least one signal having a variablephase shift which is proportional to the amplitude variations of saidinput signal; means for amplifying said provided signals; and an outputcircuit connected to perform a vector summation of all the respectiveamplified signals for producing an output signal which reproduces saidinput signal in amplified form.

7. An amplifying system for a radio frequency input signal comprising incombination: circuit means for converting said input signal into twointermediate signals having a predetermined phase relationship with theamplitude of said input signal; first and second constant gain means foramplifying each of said intermediate signals; means for combining theamplified signals from said first and second amplifier means; and loadmeans operably connected to said combining means for providing an`output signal in accordance with the summation of signals therebyproviding an output signal to reproduce said input signal in amplifiedform.

8. A radio frequency amplifier circuit for an amplitude varying inputsignal comprising: input terminals and output terminals; electricalcircuit means operably connected to said input terminals for convertingsaid input signal into at least two intermediate signals shifted inphase with respect to said input signal including means for varying thephase of at least one of said intermediate signals pro- Dortionately tothe amplitude of said input signal; amplifier means coupled to saidcircuit means for amplifying each of said intermediate signals topredetermined levels; and isolating combiner means coupled to saidamplifier means for summing said intermediate signals to produce anoutput signal which reproduces said input signal in amplified form.

9. An amplifier system comprising: phase splitter means responsive to anamplitude varying input signal for producing two quadrature signalcomponents of said input si-gnal; first amplifier means connected tosaid phase 'splitter means for amplifying one of said signal componentsin substantially linear relationship with respect to the amplitude ofsaid input signal; second amplifier means connected to said phasesplitter means for limiting the other quadrature lsignal component to asubstantially predetermined constant level; adder means connected tosaid first and said second amplifier for providing first and secondsignals produced as a result of a vector summation of said twoquadrature signal components amplified by said first and said secondamplifiers; a third amplifier connected to said adder means foramplifying said first signal; a fourth amplifier connected to said addermeans for amplifying said second signal; and an untuned, isolatingcombiner network connected to said third and fourth amplifier forreproducing said input signal in amplified form 'by vectoriallycombining said first and second signals into an output signal.

10. A radio frequency amplifier system comprising in combination: inputmeans for receiving an input signal having amplitude variations; circuitmeans for producing two components of said input signal which arerelated in phase relationship such that said components are separatedlby a fixed phase difference; a linear amplifier coupled to said circuitmeans for producing a signal varying in arriplitude as a function of theamplitude 'variations of said input signal; limiter amplifier meanscoupled to said circuit means to receive the other of said twocomponents for providing a signal having a substantially constantamplitude with respect to amplitude variations of said input signal;first combiner means for producing two signals varying in phaserelationship as a function of the amplitude variations of said inputsignal as a result components which are related to the amplitudevariationsv of said input sign-al.

r11. The amplifier system of claim 10, wherein said second combinermeans includes transformer means interconnected to provide a hybridcircuit of substantially constant load impedance to said high efficiencyamplifier means.

References Cited by the Examiner UNITED STATES PATENTS 2,210,028 8/1940Dohenty 330-124 X 2,548,855 4/1951 Bartelink 330-124 X 2,703,380 3/1955Fraser 328--133 X 2,751,555 6/1956 Kirkpatrick 328-134 X 2,763,8309/1956 Pihl 328-155 X 2,774,038 12/1956 Stavis 328-133 3,092,736 6/1963Ernyei 328--133 X ROY. LAKE, Primary Examiner.

R. P. KANANEN, Assistant Examiner.

1. AN ELECTRICAL SIGNAL AMPLIFYING SYSTEM HAVING INPUT AND OUTPUTTERMINALS COMPRISING IN COMBINATION: CIRCUIT MEANS OPERABLY CONNECTED TOSAID INPUT TERMINALS FOR CONVERTING AMPLITUDE VARIATIONS IN A SIGNALAPPLIED TO SAID INPUT TERMINALS INTO A PLURALITY OF SIGNALS, SAIDPLURALITY OF SIGNALS INCLUDING ONE SIGNAL WHICH VARIES IN PHASE AS AFUNCTION OF SAID AMPLITUDE VARIATIONS; AMPLIFIER MEANS OPERABLYCONNECTED TO SAID CIRCUIT MEANS FOR INDIVIDUALLY AND SEPARATELYAMPLIFYING EACH OF SAID PLURALITY OF SIGNALS; AN ISOLATING COMBINERMEANS COUPLED TO SAID AMPLIFIER MEANS FOR COMBINING SAID PLURALITY OFSIGNALS AMPLIFIED INTO AN OUTPUT SIGNALS WHICH VARIES IN AMPLITUDEACCORDING TO SAID SIGNALS APPLIED TO SAID INPUT TERMINALS.